Laser assisted system and method for bonding of surfaces; microcavity for packaging mems devices

Abstract

The present application relates to a system ( 51 ) and method for bonding surfaces that allows the production of microcavities suitable for accommodating MEMs devices or other devices that require cavity encapsulation or sealing. Laser directing means ( 55 ) are used to selectively direct a laser beam ( 53 ) onto an area of a surface to selectively heat the area of the surface in thermal contact with a curable adhesive to cause the curable adhesive to bond to the surface. The laser may be directed to the curable adhesive using a mask ( 57 ), optical manipulation of the beam ( 53 ) or a combination of these techniques. The system and method reduce the stressing of the substrate by targeting the heat onto the areas, which require heat to cure the adhesive.

1 . A system for bonding surfaces, the system comprising:
 a laser; and   laser directing means for selectively directing a laser beam onto an area of a surface to selectively heat the area of the surface in thermal contact with a curable adhesive to cause the curable adhesive to bond to the surface.   
     
     
         2 . A system as claimed in  claim 1  wherein, the laser directing means comprises a lens for focussing the laser beam onto the area of the surface. 
     
     
         3 . A system as claimed in  claim 1  wherein, the laser is adapted to produce a patterned beam which is configured to illuminate the position of the curable adhesive on the substrate. 
     
     
         4 . A system as claimed in  claim 1  wherein, the laser directing means comprises a transmission mask. 
     
     
         5 . A system as claimed in  claim 1  wherein, the laser directing means comprises scanning means for scanning the laser across the surface in a predetermined pattern. 
     
     
         6 . A system as claimed in  claim 1  wherein, the curable adhesive is arranged in a predetermined pattern. 
     
     
         7 . A system as claimed in  claim 1  wherein, the laser directing means comprises an array of laser sources. 
     
     
         8 . A system as claimed in  claim 7  wherein, the array is configured to allow a plurality of the laser sources in the array to be activated to form a predetermined pattern of illumination. 
     
     
         9 . A system as claimed in  claim 7  wherein, the array of laser sources is arranged in a set pattern. 
     
     
         10 . A system as claimed in  claim 4  wherein, the transmission mask is aligned with the curable adhesive predetermined pattern. 
     
     
         11 . A system as claimed in  claim 1  wherein, the curable adhesive is a polymer. 
     
     
         12 . A system as claimed in  claim 1  wherein the curable adhesive is a thermoplastic polymer. 
     
     
         13 . A system as claimed in  claim 1  wherein, the curable adhesive is a thermosetting polymer. 
     
     
         14 . A system as claimed in  claim 1  wherein, the curable adhesive is a photopolymer. 
     
     
         15 . A system as claimed in  claim 1  wherein, the curable adhesive is benzocyclobutene. 
     
     
         16 . A system as claimed in  claim 1  wherein, the curable adhesive is patterned such that a cavity is formed between bonded surfaces, the cavity being bounded, at least in part by the curable adhesive. 
     
     
         17 . A system as claimed in  claim 16  wherein the cavity is a microcavity that is suitable for containing a MEMS device. 
     
     
         18 . A system as claimed in  claim 1  wherein, the laser has an output beam with a substantially uniform power distribution or exposure incident upon the surface. 
     
     
         19 . A system as claimed in  claim 1  wherein, a mechanical load is applied to the surface during bonding of the curable adhesive. 
     
     
         20 . A system as claimed in  claim 1  wherein, the system further comprises a laser transmission layer that extends across the substrate. 
     
     
         21 . A system as claimed in  claim 1  wherein, the system further comprises a laser energy absorber layer. 
     
     
         22 . A method for bonding surfaces, the method comprising the steps of:
 depositing a curable adhesive onto the surface or between two surfaces; and   directing a laser beam onto the surface to selectively heat the area of the surface in thermal contact with the curable adhesive to cause the curable adhesive to bond to the surface.   
     
     
         23 . A method as claimed in  claim 22  wherein, the laser beam is directed using a lens for focussing the laser beam onto an area of the surface. 
     
     
         24 . A method as claimed in  claim 22  wherein, the laser beam cross sectional area is larger than the sample size. 
     
     
         25 . A method as claimed in  claim 22  wherein, the laser is adapted to produce a patterned beam which is configured to illuminate the position of the curable adhesive on the substrate. 
     
     
         26 . A method as claimed in  claim 22  wherein, the laser beam is directed using a transmission mask. 
     
     
         27 . A method as claimed in  claim 22  wherein, the curable adhesive is arranged in a predetermined pattern. 
     
     
         28 . A method as claimed in  claim 27  wherein, the transmission mask is aligned with the curable adhesive predetermined pattern. 
     
     
         29 . A method as claimed in  claim 22  wherein, the laser is scanned across the surface in a predetermined pattern. 
     
     
         30 . A method as claimed in  claim 22  wherein a plurality of the laser sources are provided in an array which are activated to form a predetermined pattern of illumination. 
     
     
         31 . A method as claimed in  claim 30  wherein, the array of laser sources is arranged in a set pattern. 
     
     
         32 . A method as claimed in  claim 22  wherein the curable adhesive is positioned between two surfaces and is of sufficient thickness so as to separate the surfaces and form a gap between the surfaces. 
     
     
         33 . A method as claimed in  claim 22 , the curable adhesive is patterned such that a cavity is formed, the cavity being bounded, at least in part by the curable adhesive. 
     
     
         34 . A method as claimed in  claim 22  wherein, a mechanical load is applied to the surface during bonding of the curable adhesive. 
     
     
         35 . A method as claimed in  claim 22 , the method further comprises the step of, prior to directing a laser beam onto the surface, pre-bonding the surface with the curable adhesive. 
     
     
         36 . A method as claimed in  claim 35  wherein, the pre-bonding step comprises curing the adhesive at a temperature lower than that required to fully bond the adhesive using laser heating. 
     
     
         37 . A method as claimed in  claim 35  wherein, the pre-bonding step occurs under vacuum conditions, below standard atmospheric pressure. 
     
     
         38 . A method as claimed in  claim 37  wherein, the pre-bonding step occurs in a vacuum chamber. 
     
     
         39 . A microcavity for packaging MEMS devices, the microcavity comprising:
 a first boundary surface;   a second boundary surface bonded to the first boundary surface by means of a curable adhesive; and   wherein the curable adhesive is selectively deposited between the boundary surfaces to form a cavity separating the first and second boundary surfaces and wherein   the curable adhesive is cured by selectively directing a laser beam onto the first or second boundary surface to selectively heat an area of the surface in thermal contact with a curable adhesive to cause the curable adhesive to bond to the surface.   
     
     
         40 . A microcavity as claimed in  claim 39  wherein, the curable adhesive has a thickness of at least 1 micron. 
     
     
         41 . A microcavity as claimed in  claim 39  wherein, the curable adhesive has a thickness of between 1 and 150 microns. 
     
     
         42 . A microcavity as claimed in  claim 39  wherein, the curable adhesive is patterned such that a cavity is formed, the cavity being bounded, at least in part by the curable adhesive. 
     
     
         43 . A microcavity as claimed in  claim 39  wherein, the microcavity is suitable for containing a MEMS device. 
     
     
         44 . A microcavity as claimed in  claim 39  wherein the curable adhesive is patterned in a ring shape. 
     
     
         45 . A microcavity produced using the system of  claim 1 . 
     
     
         46 . A microcavity produced using the method of  claim 22 .